At least one roll of a standard double roll stand has its ends carried in journal blocks that can slide in normally vertical guides of the roll-stand frame. In order to adjust roll spacing either between runs or during a run it is necessary to displace at least one of the rolls relative to the other. To do this enormous pressures must be brought to bear between these blocks and the frame.
Thus a system is known where each side of the frame is provided with a coaxial drive arrangement formed by a coaxial heavy-duty motor and transmission, and a spindle threaded in a nut in the frame. Each spindle is fixed to the respective transmission output and is coupled to the respective journal block so that when the spindle is rotated by the motor through the transmission in one direction it advances the respective block and when rotated oppositely it retracts it. Such a system is quite bulky and expensive. It is necessary to trade off between adjustment speed and accuracy of placement, as the single drive can not make fine adjustments if it is built for high-speed adjustment and vice versa.
Thus systems have been developed with separate coarse- and fine-adjustment drives having respective drive motors. The coarse-adjustment drive rotates a shaft parallel to the roll being adjusted and is connected to the spindles at the ends of this roll by means of bevel-gear systems and appropriate transmissions. This main drive motor is connected via a clutch to this transverse main shaft, and the secondary drive motor for fine adjustment is connected via a stepdown transmission to it also.
Thus the heavy-duty motor can be effective to approximately set the roll position, at high speed, then it is disconnected and the secondary drive motor is connected up to the main drive shaft so it can make the last adjustments at slow speed. Such a system is quite complex, as the clutches must be able to transmit considerable torque, so they are bulky and expensive. In addition the necessary structure for such a system is quite large, making it difficult to fit such a system to the roll stand which itself is quite bulky.